Modelling the kinetics of buffer reactions for rapid field predictions of lime requirement

2002

R.A. Viscarra Rossel and A.B. McBratney
Australian Centre for Precision Agriculture, McMillan Building A05, The University of Sydney NSW 2006, Australia.

Geoderma, 114: 49-63.

ABSTRACT

This research pertains to the modelling of the kinetic of soil:lime-requirement buffer reactions. These reactions were characterised using different, though not incompatible techniques. First, using two separate log-linear functions, each with a single rate coefficient, that characterise the first-order nature of the reactions and second, using a continuous double-exponential model with two rate coefficients. The former approach to kinetic modelling has been reported in the literature for various ions, e.g. potassium. Both types of modelling described the sequential, biphasic nature of the soil:lime-requirement buffer reactions, however the continuous model predicted the reactions more accurately. That is, it represented the ion exchange reaction of the agricultural soils used in the study in a more accurate manner than the two separate log-linear functions. A simple algorithm was devised to predict equilibrium pHbuffer measurements at much shorter times than those suggested in the literature. The methodology used pHbuffer measurements of the first 3 s of the ongoing reactions to predict equilibrium pHbuffer values, which occurred at 12 minutes. Prediction accuracy was 0.1 pHbuffer units and the bias was low. Ultimately, the technique may be incorporated into the data acquisition and data handling algorithms of a soil pH and lime-requirement sensing system for field-based predictions of lime requirement and continuous liming.